1. Field of the Invention
The present invention relates to a kind of high strength polyethylene fiber, especially a kind of colored high strength polyethylene fiber, and their preparation method and application.
2. Description of Related Art
High strength polyethylene (HS-PE) fibers are well known synthetic fibers with high strength and modulus, and are produced from ultrahigh molecular weight polyethylene (UHMWPE) with a molecular weight higher than 1,000,000. Right now, HS-PE fibers, Aramid fibers and carbon fibers are considered as three high performance fibers in the world. Due to its high strength, high modulus and low density, the UHMWPE fiber plays an important role not only in modern warfare, defense equipment and aerospace field, but also in civil fields.
Conventionally, HS-PE fibers are mostly produced from UHMWPE by the so-called gel-spinning and ultra-heat drawing processes. However, during these two processes, the UHMWPE, as long, flexible macromolecule chains, has a tendency to be entangled together. In order to avoid this problem, the UHMWPE has to be dissolved in a solvent, which could enlarge the distance of macromolecule chains by diluting the concentration of the UHMWPE. HS-PE fibers with extended chains could be obtained by ultra-heat drawing and molecule tropism of UHMWPE gel precursor fibers with moderate macromolecule entanglement points. The method mainly has five steps: (1) getting a spinning solution by solving UHMWPE in a solvent; (2) getting solvent-embedded wet precursor fibers with moderate molecular chain entanglements by extruding the solution from a spinneret hole and quenching curing in air or water; (3) removing the solvent by certain extraction solvent; (4) drying the precursor fibers in an oven; and (5) getting HS-PE fibers with extended chain crystal by ultra-heat drawing of the precursor fibers.
Japanese Patent No. 7-238416 discloses a method for preparing HS-PE fibers by evaporating a solvent actively during a dry-spinning process, and its specific process includes dissolving UHMWPE (5˜50%) in a volatile solvent (95˜50%) first and then transferring precursor fibers obtained by thermal extrusion through a spinning cylinder. During this process, more than 40% of the solvent is evaporated by continually purging stable hot air flow into the cylinder. Residual solvent can be removed during a heat-drawing process. In this patent, the spinning adhesion problem could be solved by forming semi-dry precursor fibers through actively removing partial solvent in the spinning process. However, because the solvent evaporation happens in both spinning and heat-drawing processes, fireproofing and explosion-proofing and solvent recovery must be carried out separately during the spinning and drawing processes. Obviously, these operations increase the investment in equipment and make the solvent recovery more difficult, which are unfavorable for large-scale industrial production.
High-strength is the main goal of the prior art processing technology, resulting in HS-PE fibers which have tensile strength mostly larger than 30 cN/dtex and are in white color. Due to the complexity of the production process and high price, HS-PE fibers are usually used in military field. However, polyethylene fibers with a tensile strength ranging from 15 to 30 cN/dtex could already meet the requirements of applications in civil fields. Therefore, it is a waste of fiber performance and resources to use polyethylene fibers with a tensile strength higher than 30 cN/dtex in civil fields. And the increase of cost limits the application of polyethylene fibers with a tensile strength higher than 30 cN/dtex in civil fields. In addition, in certain application fields, such as rope nets, there is usually requirements for colors. However, it is difficult to color these fibers by general methods because there are no other functional groups in UHMWPE's macromolecular chains except for the C—H bond, with which is hard to combine dye molecules. No work has been reported on methods for preparing colored HS-PE fibers.